lecture by prof s s murthy 19th feb - silicon institute of...

WIND ENERGY SYSTEMS (WES)

FOR POWER GENERATION

Lecture By

Prof S S Murthy

19th Feb.2015

Silicon Institute of Technology,

Bhubaneswar

National Workshop on

Emerging Technologies in Electrical Engineering,

THERITICAL POTENTION of

Renewable Energy

RENEWABLES

ARE SOMETIMES DESCRIBED AS

• THE “DREAMS OF THE 1970S,

• REALITIES BUT LUXURIES OF 2000,

• AND THE NECESSITIES OF 2020 AND THEREAFTER”

INCLUDE HYDROPOWER, BIOMASS, SOLAR, WIND, GEOTHERMAL AND OCEAN RESOURCES

RENEWABLE POWER CAPACITIES(GW) IN WORLD ,

EU -27, BRICS, AND TOP SIX COUNTRIES , 2012

ALL INDIA GENERATING INSTALLED CAPACITY (MW)

(As on 31-12-14 )

(source: CEA)

GE – Wind Energy

1.5 MW Turbine

WIND ENERGY

GRID CONNECTED

WIND ENERGY SYSTEM

CHITRADURGA-KAR

Global cumulative growth of wind power capacity

Global investment to 2050 (USD billion)

Progress in wind power since

2008

Global wind map, installed capacity and production for lead

countries

Wind generation is significant

In 2010 alone, new global wind power

installations equaled the capacity of 66

large conventional power plants.

World Wind Energy Scenario

TECHNICAL POTENTIAL OF ONSHORE WIND ENERGY IS

ABOUT 20000 TO 50000 TWH PER YEAR AGAINST THE

TOTAL WORLD ELECTRICITY CONSUMPTION OF 15000

TWH

ECONOMIC POTENTIAL DEPENDS ON FACTORS LIKE

AVERAGE WIND SPEED, STATISTICAL WIND SPEED

DISTRIBUTION, TURBULENCE INTENSITIES AND COSTS

OF WIND TURBINE SYSTEMS

WORLD WIND ENERGY

SCENARIO

AS ENERGY OF WIND IS PROPORTIONAL TO THIRD POWER OF WIND SPEED, ECONOMIC CALCULATIONS ARE SENSITIVE TO LOCAL AVERAGE WIND SPEED

BECAUSE THE WIND ENERGY IS INTERMITTENT, WIND TURBINES MAINLY DELIVER ENERGY BUT VERY LITTLE CAPACITY.

TYPICAL CAPACITY VALUES BEING OFTEN LESS THAN 20% OF INSTALLED WIND POWER

WINDIEST REGIONS, POTENTIAL

COASTAL REGIONS OF AMERICAS, EUROPE, ASIA, AUSTRALIASIA

TOTAL RESOURCE IS VAST- ONE ESTIMATE PUTS IT AS A MILLION GW

Even if only1% of area used with a low load factor of 15-40%, wind potential correspond to total capacity of all elec. Generating plants

Offshore resource HUGE- capable of supplying all EU electricity without going further than 30km offshore.


AS THE PENETRATION OF WIND TURBINES INCREASES THE PERCENTAGE FALLS FURTHER, REQUIRING EVEN MORE BACK UP POWER FOR A RELIABLE ENERGY SUPPLY

IT IS POSSIBLE TO TRANSFORM WIND-GENERATED ELECTRICITY FROM INTERMITTENT TO BASE LOAD POWER IF IT IS COMBINED WITH COMPRESSED AIR ENERGY STORAGE. THUS A HIGHER CAPACITY FACTOR CAN BE ACHIEVED WITH SMALL ECONOMIC PENALTY


BY OPTIMIZING THE TURBINE CHARACTERISTICS TO THE LOCAL WIND REGIME, CAPACITY FACTOR CURRENTLY OFTEN AT 20-25% CAN BE OPTIMIZED WITHOUT LOOSING TOO MUCH ENERGY OUTPUT.

HOWEVER EXTREME CAPACITY FACTORS OF ABOUT 40% AUTOMATICALLY MEAN A LARGE LOSS OF POTENTIAL ENERGY OUTPUT


BECAUSE OF SCARCITY OF LAND IN URBAN CENTERS, THE COUNTRIES LIKE DENMARK, NETHERLANDS, UK AND SWEDEN ARE DEVELOPING OFFSHORE PROJECTS

A UNDP STUDY ESTIMATES THAT AROUND 3000 TWH PER YEAR OF ELECTRICITY COULD BE GENERATED IN THE COASTAL AREAS OF EUROPEAN UNION

World Wind Energy Scenario:

Wind Turbine Sizes

THE CURRENT WIND ENERGY ERA BEGAN

IN MID 1970S WITH A TYPICAL SIZE OF A

WIND TURBINE OF 30 KW WITH A ROTOR

DIAMETER OF 10 METERS

THE LARGEST UNIT INSTALLED TODAY

HAS A CAPACITY OF 1650 KW WITH A

ROTOR DIAMETER OF 66 METERS

ATTRACTIVE WIND REGIONS

Europe- North/West coasts, Mediterranean

Asia- East coast, some inland areas

Africa- North, Southwest coast

North America- Most coastal regions, some

mountainous central zones

S. America- Best Towards south

Wind Energy Scenario

TECHNICAL POTENTIAL OF ONSHORE WIND

ENERGY IS ABOUT 20000 TO 50000 TWH PER YEAR

AGAINST THE TOTAL WORLD ELECTRICITY

CONSUMPTION OF 15000 TWH

ECONOMIC POTENTIAL DEPENDS ON FACTORS

LIKE AVERAGE WIND SPEED, STATISTICAL WIND

SPEED DISTRIBUTION, TURBULENCE INTENSITIES

AND COSTS OF WIND TURBINE SYSTEMS

World WIND ENERGY Scenario

WIND ENERGY WAS USED AS A SOURCE OF

POWER BEFORE THE INDUSTRIAL REVOLUTION

DISPLACED BY FOSSIL FUELS BECAUSE OF COST

AND RELIABILITY

OIL SHOCKS OF 1970S SAW RENEWED INTERESTS

IN WIND ENERGY FOR APPLICATIONS LIKE GRID-

CONNECTED ELECTRICITY, WATER PUMPING AND

POWER SUPPLY IN REMOTE AREAS

Wind Power Global Capacity, 1996-

2012

Wind Power Capacity and additions,

Top 10 Countries, 2012

26

Introduction

• Account for around 95% of the total supply in 2007

• Asian manufacturers improve their shares

(Goldwind & Sinovel in China, Suzlon in India)

Suzlon

10.5%

Vestas

22.8%

GE Wind

16.6%

Gamesa

15.4%

Enercon

14.0%

Siemens

7.1%

Goldwind

4.2%

Acciona

4.4%

OthersSinovel

3.4%Nordex

3.4%

Top 10 wind turbine suppliers in 2007

Wind Turbine Suppliers

Wind Power in India Estimated Potential as per CWET: 65-100 GW

Renewable share (31 GW) in overall Power Capacity (234 GW) amounts to more than 13%

Share of Wind power generation in Indian Renewables is 65 %.

India is fifth after USA, Germany, Spain, China

NOTE: Only about 20% is the maximum utility factor of installed wind capacity based on local wind conditions.

WIND POWER – State Wise

Analysis in INDIA

Wind Power Potential in India

Estimated Gross Potential

NAPCC - National Action Plan on Climate Change

REC - Renewable Energy Certificate

SERCs - State Electricity Regulatory Commissions

SNA - State Nodal Agency

IPP - Independent Power Projects

49

Wind Turbine Technology

Wind turbine size

127 6,000 2007

112-126 4,500-5,000 2004

90-104 3,000 2003

70 1,500 1998

46 600 1994

37 500 1992

30 300 1989

15 50 1985

Rotor Diameter (m) Capacity (kW) Year

MODERN WIND TURBINES

Early machines (20 Yrs. Ago)- 50-

100kW, 15-20m dia

Present trend-upto 2MW and above, 60-

70m dia

Offshore upto 5MW and 110m.dia

52

Wind Turbine Technology

Horizontal- and vertical-axis wind turbines

Rotor

Diameter

Gearbox

Generator

Rotor

blade

Tower

Nacelle

Rotor Diameter

Gearbox

Tower

Rotor

blade

Generator

Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Wind Turbine

Offshore Wind Farm

Fixed-bottom foundation and floating offshore

concepts

Wind farms

REQUIREMENTS

Area required per Wind Turbine = 5Acres (approx) Grid availability.

Accessibility for commissioning.

Strong terrain / soil for proper foundation / civil work

Favorable environmental condition to prevent

corrosion & not prone to cyclone.

Wind farms

Cluster of tens of machines or many

single machines

Economy of scale dictates wind farms-

civil Engg and grid connection cost

decreases

SITING AND CLEARANCES

GCIG IN WIND SYSTEM

INSIDE NECELLE(RRB

VESTAS)

Enercon System(SYN.GEN)

GENERATORS AND SYSTEMS

FIXED SPEED

• INDUCTION GENERATOR(MOSTLY)

• SYNCHRONOUS GENERATOR

VARIABLE SPEED WITH POWER ELECTRONIC

CONVERTORS-AC/DC/AC

• Doubly Fed Induction Generator (DFIG)

• Permanent Magnet Synch. Generator- Direct Driven

Gearless

65

Wind Energy Conversion

WES without using power converters

Soft

starter

Gearbox

SCIG

Transformer GridCapacitor

Up to 2.3 MW

Advantages • Low manufacturing cost

• Robust, low maintenance cost

Drawbacks • Low conversion efficiency

• Large fluctuation in output power

Squirrel Cage

Induction Generator

66

Doubly fed induction generator with rotor converter

Reduced-capacity

converter Transformer GridGearbox

DFIG


Up to 5 MW

Advantages

• Extended speed range

• High system efficiency and low cost because

• Decoupled active & reactive power control

• Enhanced dynamic performance

Drawbacks

• Limited grid-fault operation capability

67


Wind energy systems with full-power converters

Gearbox

SCIG

WRSG

PMSGTransformer Grid

Full power

converter

Up to 5 MW

(PMSG)

Advantages

• The generator fully decoupled from the grid

• Wide speed range

• Smooth grid connection

• Reactive power compensation

• Capability to meet the strict grid code

Drawbacks

• High system cost, reduces system efficiency

FIXED SPEED WIND SYSTEMS

SCHEMATIC OF A CONSTANT

SPEED WIND SYSTEM

INDUCTION

GENERATOR

WIN

D

TU

RB

INE

GE

AR

BO

X

11kV

GRID

CAPACITOR

TRANSFORMER

415V 11kV

P

P

Q

Enercon wind system

E-48 TECHNICAL DATA Rated capacity : 800 kW Rotor diameter : 48 m Hub height : 56.85m and 74.85 m Rotor with Pitch Control Type : Upwind rotor with active pitch control Direction of rotation : Clockwise Number of blades : 3 Length of blades : 20.7 m

DATA…

Swept area : 1810 m²

Blade material : Fiberglass (reinforced epoxy) with

integral lightning protection

Rotor speed : Variable, 16-31.5 rpm

Tip speed : 41 - 78 m/s

Pitch control : Three synchronized blade pitch

system with battery back-up

Enercon System….

Generator : Synchronous - Type Hub : Rigid Bearings : Tapered roller bearings Grid Feeding : AC-DC-AC through Convertor - Invertor Braking System : 3 independent Aero Brakes with emergency back up supply. Yaw Control : Active through adjustment gears, friction damping Cut-in Wind Speed : 2 m/s Rated Wind Speed : 14 m/s Tower : Steel Tubular / Concrete

POWER RELATION-WIND

P= ρCp D2 w3

• ρ = AIR DENSITY

• Cp= CONSTANT

• D= BLADE DIA

• w =WIND SPEED

POWER Vs WIND SPEED

1.0

25 20 10 5 15

Wind speed, m/s

.p.u

power

Cut in speed

Cut out

speed

Pitch Control

DOUBLY WOUND SCIG AS

WIND GENERATOR (NO

CONVERTOR)

GRID

DATA ON A WIND MACHINE

Rated Power:1.65 MW

Blade dia: 63m

Cut in speed:3-5 m/s

Cut out speed: 20-25 m/s

Energy production (MWh)

Wind speed (m/s) Energy

at 60 m height-

5m/s- 1500

7m/s 3700

8m/s 4800

GRID INTERFACE

SEVERAL PROBLEMS OF EVACUATION

OF ENERGY INTO THE GRID

HIGH WIND AND LOW LOAD

CONDITIONS

WEAK , UBNORMAL GRIDS

SEVERAL STUDIES MADE

GRID CONNECTED

INDUCTION GENERATOR

COMPARISON- MOTOR Vs

GEN

MOTOR GENERATOR

STATOR VOLTAGE VS VS

STATOR CURRENT IS -IS

MAGNETIZING

CURRENT

IM IM

AIRGAP VOLTAGE VG VG

MOTOR Vs GEN.

MOTOR GENERATOR

ROTOR

CURRENT

IR -IR

SLIP s -s(=s')

AIR GAP

POWER (Pg) s

RI3 r2

r s'

RI3 r2

r

Motoring and Generating

MOTOR GENERATOR

Pshaft

DEVELOPED

TORQUE (Td)

SPEED (pu)

s1s

R

ω

3IP r

s

2

rout

out

r

s

2

rin

Ptoopp

s'1s'

R

ω

3IP

s

R

ω

3I r

s

2

r

s'

R

ω

3I

s

R

ω

3I r

s

2

rr

s

2

r

s1υ s'1υ

Motoring/Generating

MOTOR GENERTOR

Pmech

Pelec

s1sω

R3I

s

2

r

s'1sω

R3I

s

2

r

sss cosI3V sss cosI3V

MOTOR GENERATOR

Pg

Pe

lec

PoutTd ν

TL

LoadPmech

Pg

Pe

lec

Pm

PinTd ν

Tin

PRIME

MOVER

GRID CONNECTED INDUCTION

GENERATORS DRIVEN BY WIND/HYDRO

TURBINES

Induction Generators ( I G ) are used for low

and medium power generation, as they

have certain inherent advantages over

conventional alternators

Low unit cost

Less maintenance

Rugged and brushless rotor

Asynchronous operation

THE INPUT POWER TO THE GENERATOR CAN BE

NORMALLY KEPT CONSTANT WITH HYDRO

TURBINES.

THE WIND TURBINE ON THE OTHER HAND

PROVIDES VARYING POWER INPUT DEPENDENT

ON THE WIND SPEED.

CAPACITORS ARE CONNECTED TO THE

GENERATOR TERMINALS , TO IMPROVE THE

SYSTEM POWER FACTOR AND TO REDUCE THE

VAR DRAIN FROM THE GRID

PROBLEM WITH THE GRID

GRID FAILURE

SINGLE PHASING

TURBINE OVERSPEED WITH LOAD THROW OFF(ABOVE 2pu)

GENERATOR THERMAL OVERLOAD

POOR POWER QUALITY OF GRID-VOLTAGE, FREQUENCY

SELF EXCITATION DUE TO CAPACITOR DUE TO GRID FAILURE AND TURBINE OVERSPEED

Grid connected induction

generator

EQUIVALENT CIRCUIT OF IG

FIND RESPONSE AT CONSTANT POWER

INPUT AND GRID VOLTAGE

USE THEVENIN EQ. CIRCUIT

THEVENIN EQUIVALENT

CIRCUIT

Pin=- 3Ir2 Rr (1-s)/s…………(1)

Vth+ (Rth+ Rr /s +j Xth ) Ir =0……….(2)

ABOVE ARE TWO EQS WITH TWO

UNKNOWNS s AND Ir

FROM FIG.

Ir= Vth / {[Rth + Rr /s ]2 + Xth2} 1/2

SIMPLIFYING

As2 +Bs + C =0

A= Rth2 + Xth

2 - 3Vth 2/ Pin

B=2Rth Rr +3 Vth / Pin

C= Rr 2

Pin=- 3Ir2 Rr (1-s)/s

SINCE s IS NEGATIVE Pin IS

POSITIVE

SOLVE FOR s, FOR GIVEN POWER INPUT AND GRID VOLTAGE

SOLVE EQ. CIRCUIT

GET ACTIVE POWER

REACTIVE POWER

POWER FACTOR

EFFICIENCY

DATA ON PRACTICAL FIELD

SYSTEMS

GENERATOR- 415V, 50 Hz

GRID-11kV, 50 Hz

TRANSFORMER IMPEDANCE- (0.021+j0.382)p.u

HV- TRANS. LINE IMPEDANCE- (0.021+j0.382)Ohm/km

SC MVA OF GRID = 250

LENGTH OF HV LINE=10km (HYDRO), 2km(WIND)

EQ. CKT. PARAMETERS(pu)

M/C Rs Rr xls xlr xm Rc

1 0.0135 0.024 0.105 0.169 3.34 72.2

2 0.19 0.0164 0.069 0.087 3.0 47.85

3 0.0504 0.0493 0.076 0.132 2.35 32.8

4 0.031 0.0256 0.0657 0.094 2.08 42.5

5 0.0492 0.031 0.933 0.179 3.19 52.42

CHARACTERISTICS OF WIND

TURBINE DRIVEN 55/11KW

INDUCTION GENERATOR

EFFECT OF VARIATION OF GRID

VOLTAGE

EFFECT OF VARIATION OF TERMINAL CAPACITOR

EFFECT AT VARYING POWER INPUT

References..

S.S.Murthy (with C.S.Jha and P.S.N.Rao), "Analysis of Grid Connected Induction Generator driven by Hydro/ Wind Turbines under Realistic System Constraints ", IEEE Trans. on Energy Conversion, March, 1990 Volume 5, No. 1, pp 1-7

S.S.Murthy (with A.H.Ghorashi, B.P.Singh & Bhim Singh), 'Analysis of Wind Driven Grid Connected Induction Generators under unbalanced Grid Conditions', IEEE Trans. on Energy Conversion Vol.9, No.2, June, 1994 pp 217-223

S.S.Murthy (with C.S.Jha, A.H.Ghorashi, P.S.Nagendra Rao), 'Performance Analysis of Grid Connected Induction Generators Driven by Hydro/Wind Turbines including Grid Abnormalities', presented at Inter Society Energy Conversion Engg. Conference (IECEC at Washington DC, Aug., 1 989).

VARIABLE SPEED WIND SYSTEMS

DOUBLY FED

INDUCTION GENERATORS:

DOUBLY FED IND. MACHINE

Pe

Pm Pr

Pg Pcus

Pcur

DFIG

CONVERTOR(BIDIRECTIONAL))

TRANSFORMER

f

fr f

GRID

EQUIVALENT CIRCUIT of DOUBLY

FED WOUND ROTOR I.M- MOTRING

Is

Vs

Rs jxls

Rc xm

I0

Ic Im

Vg Ej sVg

Ir

Rr+jsXlr

sPg= Pr + Pcur

Pg= Pr + (1-s) Pg +Pcur

ROTOR EQUATION

sVg- Ir(Rr+jsxlr)-Ej=0

sVg= Ir(Rr+jsxlr)+Ej

sVg-Ej = Ir(Rr+jsxlr )

(Ej REF. TO STATOR TURNS)

DFIG (COVERTOR IN ROTOR)

POWER SPEED CURVES

0 1 2 3 4 5 6 70

20

40

60

80

Generator Speed (rad/sec)

Tu

rbin

e P

ow

er (

kW

)Vw=11m/s

Vw

=10m/s

Vw

=9m/s

Vw

=8m/s

Vw

=7m/s

Vw

=6m/s

Vw

=5m/s

Maximum Power Line

Mechanical power output of the wind turbine vs. generator speed for different wind speeds

PHASOR DIAGRAM WITH

INJECTED EMF

Ej

sVg

Ir

β

Φr

RESOLVE VOLTAGES AND DROPS

ALONG Ir AXIS

sVg cos Φr= Ir Rr+ Ej cos (Φr + β)

sVg Ir cos Φr= Ir2 Rr+ Ir Ej cos (Φr + β)

ON 3- PH BASIS

Pg= 3 Vg Ir cos Φr

Pcur=3 Ir2 Rr

Pr= POWER FED TO CONVERTOR

=3 Ir Ej cos (Φr + β)

AIRGAP POWER=

• ROTOR COPPER LOSS+ POWER FED TO

CONVERTOR + MECHANICAL POWER

EXAMPLE

s= - 0.2

Pg=+100

Pm, = +120

Pr =-20 (POWER FED TO ROTOR)

Pe, = +100

POWER DRAWN FROM GRID

=Pgrid = 120

MODE-I, SUBSYNCHRONOUS,

MOTORING

0<s <1, s IS +VE

Pg, Pm, Pe, Pr POSITIVE

Pm =(1-s) Pg IS POSITIVE

NEGLECT LOSSES Pcur, Pcus

EXAMPLE

s= +0.2

Pg=+100

Pm, = +80

Pr =+20

Pe, = +100

POWER DRAWN FROM GRID

=Pgrid = 80

MOTORING AT s=0.2

Pe

(100)

Pm(80) Pr

(20)

Pg

(100)

Pcus Pcur

DFIG

TRANSFORMER

f

fr f

GRID (80)

CONVERTOR

MODE-II, SUPERSYNCHRONOUS,

MOTORING

-1<s <0, s IS NEGATIVE

Pg, Pm, Pe, POSITIVE

Pr NEGATIVE

Pm =(1-s) Pg IS POSITIVE

NEGLECT LOSSES Pcur, Pcus

Pm IS MORE THAN Pg

MOTORING AT s= -0.2

Pe

(100)

Pm(120) Pr

(-20)

Pg

(100)

Pcus Pcur

DFIG

TRANSFORMER

f

fr f

GRID (120)

CONVERTOR

MODE-III, SUBSYNCHRONOUS,

GENERATING

0<s <1, s IS +VE

Pg, Pm, Pe, Pr NEGATIVE

Pm =(1-s) Pg IS NEGATIVE

Pm IS LESS THAN Pg

EXAMPLE

s= + 0.2

Pg=-100

Pm, = -80

Pr =-20 (POWER FED TO ROTOR)

Pe, = -100

POWER FED TO GRID

=Pgrid = 80

GENERATING AT s= +0.2

Pe

(-100)

Pm(-80) Pr

(-20)

Pg

(-100)

Pcus Pcur

DFIG

TRANSFORMER

f

fr f

GRID (-80)

CONVERTOR

MOTORING

GENERATING

MODE-IV, SUPERSYNCHRONOUS,

GENERATING

-1<s <0, s IS NEGATIVE

Pg, Pm, Pe, NEGATIVE

Pr POSITIVE

Pm =(1-s) Pg IS NEGATIVE

Pm IS MORE THAN Pg

EXAMPLE

s= - 0.2

Pg=-100

Pm, = -120

Pr =+20 (POWER DRAWN FROM ROTOR & FED TO GRID)

Pe, = -100

POWER FED TO GRID

=Pgrid = 120

GENERATING AT s=-0.2

Pe

(-100)

Pm(-120) Pr

(+20)

Pg

(-100)

Pcus Pcur

DFIG

TRANSFORMER

f

fr f

GRID (-120)

CONVERTOR

GENERATING

POWER Vs SLIP (MOTORING)

0 s -1

Pr

Pm Pg

s

POWER Vs SLIP, GENERATING

0 s

-1

s 0

Pr Pm Pg

Pg Pm Pr

MOTOR SUB

SYNC

+ + +

MOTOR SUPER

SYNC

+ + -

GENERATOR SUB

SYNC

- - -

GENERATOR SUPER

SYNC

- - +

PM GENERATORS

WIND SYSTEM WITH

PM GENERATOR

INVERTER RECTIFIER

TRANSFORMER

WHAT IS IN STORE FOR

FUTURE?

FUTURE IN WIND ENERGY

FIXED SPEED SCIG (UPTO 1 MW)

VARIABLE SPEED SCIG (WITH

CONVERTOR/INVERTOR BETWEEN MACHINE AND

GRID

DFIG (FEW MW)

SYNCH GEN LOW SPEED GEARLESS WITH AC-DC-AC

PM SYNCH GEN WITH AC-DC-AC

FUTURE IN INDIA

NEW PREDICTION: 100GW

INCREASE HEIGHTS

RETROFIT OLD FARMS

WIND FORECASTING

OFF-GRID

OFF-SHORE (HUGE POTENTIAL)

FUTURE DEVELOPMENTS

GERMANY, DENMARK- SLOWED DOWN

USA, SPAIN,INDIA, CHINA FORGING AHEAD

CANADA, MIDDLE EAST, FAR EAST, S. AMERICA HAVE GOOD PLANS

At current growth 150GW of wind power expected in 2010

FACTORS FOR GROWTH

POLITICAL SUPPORT

INTERNATIONAL COMMITMENT

CONCERN FOR CLIMATE CHANGE, EMISSIONS

TECHNOLOGY FAIRLY MATURE

PERFORMANCE AND COST ARE NOW CRUCIAL

THANK YOU

lecture by prof s s murthy 19th feb - silicon institute of...

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